Hi,
Servo by definition is "Closed Loop", so its all about feedback. What servos are you trying to run? Some servos rely on encoders, serial coders, resolvers, sync pulses, etc.
Could it be a feedback issue?
Also, different servos have different specs - It would depend on how close you are to the specs.
I have seen different types of servos get very hot when run on a same drive. I don't understand the difference in signals with all amps, but fanuc for example...... You might be able to run an aM30/3000 on one amp, but you could burn up an a30/3000.
If you are not using feedback, You can still run a servo with an Inverter (AC Drive - Just you cant always test feedback)
I hacked an inverter (tore out the Bus, and built a variable Bus, and wired it back into the inverter). This allowed me to run virtually any servo motor (too a degree). The trick was to start with 0 volts on bus and 0 speed. Gradually, i increased both to make the motor run smoothly and speed up. If I increased too much on speed or Bus voltage, the motor would chatter.
In Short, I think your problem is either feedback (if you are using it), or PWM.
Dos the motor do anything at all? Does it chatter?